VB6 Host with MFC DLL Showing Modal Dialog Incorrectly

Question

We have a VB6 application that we have provided extended functionality through an MFC DLL. However, there's a specific problem with CDialog-based classes in the DLL. We pass in Me.hWnd from the VB6 app's main form to give to the CDialog constructor so that DoModal() knows what its parent is. Although the CDialog-based classes are staying on top of the VB6 app on DoModal(), they do not block the VB6 app the way that's expected by a modal dialog. That is, while the DLL dialog remains in front of the EXE's window, I can still click the button that called the DLL, showing the dialog again (and again).

There's not much to show from the VB6 code. As I mentioned it just passes in Me.hWnd. The MFC code is simple enough:

HWND exeHwnd = pSessionContext->GetHWnd(); // our state container for the DLL
CWnd* exeWnd = CWnd::FromHandle(exeHwnd);
MyCDialog dlg(exeWnd);
INT_PTR result = dlg.DoModal();
// waits, stays in front, but does not "block" the window
switch (result) // ...

I traced the values along the way and confirmed window handles with Spy++. Everything seems to be fine. Any ideas what I'm missing or doing wrong?

ADDITIONAL INFO

That hwnd value is used elsewhere for MessageBox and works as expected.

MarkJ MarkJ · Accepted Answer · 2012-12-31T13:52:31

A simplistic solution might be to disable the parent VB6 app in the VB6 code just before calling the DLL, and when the DLL code returns re-enable the VB6 app. Something like this (air code)

Me.Enabled = False 
MagicDLL.ShowTheDialog(Me.hWnd)
Me.Enabled = True

VB6 Host with MFC DLL Showing Modal Dialog Incorrectly

1 Answers